Group by clause and having clause in select

Question

hi frnds
plz give me some information of group by and having clause used in select statement with example
thanks

Answer 1

The Open SQL statement for reading data from database tables is:
SELECT      <result>
  INTO      <target>
  FROM      <source>
  [WHERE    <condition>]
  [GROUP BY <fields>]
  [HAVING   <cond>]
  [ORDER BY <fields>].
The SELECT statement is divided into a series of simple clauses, each of which has a different part to play in selecting, placing, and arranging the data from the database.
You can only use the HAVING clause in conjunction with the GROUP BY clause.
To select line groups, use:
SELECT <lines> <s1> [AS <a1>] <s2> [AS <a2>] ...
               <agg> <sm> [AS <am>] <agg> <sn> [AS <an>] ...
       GROUP BY <s1> <s2> ....
       HAVING <cond>.
The conditions <cond> that you can use in the HAVING clause are the same as those in the SELECT clause, with the restrictions that you can only use columns from the SELECT clause, and not all of the columns from the database tables in the FROM clause. If you use an invalid column, a runtime error results.
On the other hand, you can enter aggregate expressions for all columns read from the database table that do not appear in the GROUP BY clause. This means that you can use aggregate expressions, even if they do not appear in the SELECT clause. You cannot use aggregate expressions in the conditions in the WHERE clause.
As in the WHERE clause, you can specify the conditions in the HAVING clause as the contents of an internal table with line type C and length 72.
Example
DATA WA TYPE SFLIGHT.
SELECT   CONNID
INTO     WA-CONNID
FROM     SFLIGHT
WHERE    CARRID = 'LH'
GROUP BY CONNID
HAVING   SUM( SEATSOCC ) > 300.
  WRITE: / WA-CARRID, WA-CONNID.
ENDSELECT.
This example selects groups of lines from database table SFLIGHT with the value ‘LH’ for CARRID and identical values of CONNID. The groups are then restricted further by the condition that the sum of the contents of the column SEATSOCC for a group must be greater than 300.
The <b>GROUP BY</b> clause summarizes several lines from the database table into a single line of the selection.
The GROUP BY clause allows you to summarize lines that have the same content in particular columns. Aggregate functions are applied to the other columns. You can specify the columns in the GROUP BY clause either statically or dynamically.
Specifying Columns Statically
To specify the columns in the GROUP BY clause statically, use:
SELECT <lines> <s1> [AS <a 1>] <s 2> [AS <a 2>] ...
               <agg> <sm> [AS <a m>] <agg> <s n> [AS <a n>] ...
       GROUP BY <s1> <s 2> ....
To use the GROUP BY clause, you must specify all of the relevant columns in the SELECT clause. In the GROUP BY clause, you list the field names of the columns whose contents must be the same. You can only use the field names as they appear in the database table. Alias names from the SELECT clause are not allowed.
All columns of the SELECT clause that are not listed in the GROUP BY clause must be included in aggregate functions. This defines how the contents of these columns is calculated when the lines are summarized.
Specifying Columns Dynamically
To specify the columns in the GROUP BY clause dynamically, use:
... GROUP BY (<itab>) ...
where <itab> is an internal table with line type C and maximum length 72 characters containing the column names <s 1 > <s 2 > .....
Example
DATA: CARRID TYPE SFLIGHT-CARRID,
      MINIMUM TYPE P DECIMALS 2,
      MAXIMUM TYPE P DECIMALS 2.
SELECT   CARRID MIN( PRICE ) MAX( PRICE )
INTO     (CARRID, MINIMUM, MAXIMUM)
FROM     SFLIGHT
GROUP BY CARRID.
  WRITE: / CARRID, MINIMUM, MAXIMUM.
ENDSELECT.
regards
vinod